The depiction of Harems in “Marco Polo” and “300” seems more like a porno than a historical reality. Do we know what life was like for any of these women? What was the point of, in the case of Montezuma II for example, of keeping literally thousands of women in a harem? In cases with so many women would the ruler in question actually have had sex with all of them? Would the women be kept around for a long time or just slept with once and then tossed out? Why would Genghis Khan keep a harem while at the same time making adultery punishable by death?
You may be interested in one of my previous answers about the Ottoman Imperial Harem, which I believe touches on most of your questions.
Of course, if you have any further questions, please let me know as I'd be glad to help!